Capercaillies are not out of the woods yet, says Jack Watkins.

Deep in the Scottish pine forest, when the male capercaillie stretches out his neck and raises his head aloft, fanning out his tail feathers and affecting a slow, lordly stride amid a circle of available females, it's as if he's performing some archaic fertility ritual of the bird world.

Weighing in at almost nine pounds, he's a giant of a bird, the largest grouse on the planet. His name derives from the Gaelic "capul coillie" (horse of the forest). Everything about his appearance is strange, fierce and rather grand – the red patch (wattle) around his eye, the pale, hooked bill, the blue-black plumage, the broad tail, and the deliberate, strolling gait. Then there is the voice, often described as sounding like the plip-plop of large drops of water, followed by the popping of a cork, though this scarcely conveys its peculiarity. His behaviour can match his appearance, too. Unpaired "rogue" males are aggressively territorial. Anything straying within his boundaries may be attacked, including humans.

But the chance of being assailed by a capercaillie is remote, for this is a species whose decline has been so long, deep and desperate that in 2003 it was declared the fastest disappearing bird in Britain. "Wode hennes" most likely once inhabited woodlands in northern English counties until wide-scale forest clearances and hunting wiped it out here, and north of the border, in the 17th and 18th centuries. The bird was successfully reintroduced to Scotland in 1837, but similar attempts in England failed. Even in Scotland, a recent study put numbers at a mere 2,000, and that could be over-optimistic.

To lose a bird once, to paraphrase Lady Bracknell, may be a misfortune, to lose it twice looks like carelessness, but this time around it certainly won't be for want of effort. In recent years, the RSPB has been a lead partner with the Centre for Ecology and Hydrology in a programme to drag the species back from the brink.

But what caused this latest decline? Capercaillie prefer native pine and mixed forests. They feed on blaeberry, pine needles and juniper and lurk in areas where, with thick undergrowth nearby for protection, they can carry out their "lekking" rituals undisturbed by intruders. Intensively managed modern plantations provide less cover, and thus less protection from predators such as foxes and crows, which feed on the chicks. Tim Poole, Capercaillie project officer – a post funded by the RSPB, Scottish National Heritage and the Forestry Commission – says that fragmentation of the old forests has had a serious impact.

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"Capercaillies are sedentary birds. Males rarely move more than five kilometres from where they hatch and the average distance of hens is 11 kilometres. This may be causing small populations to become isolated and, over time, leads to inbreeding."

Deer fences enclosing forestry plantations have proved another problem. Capercaillie are used to flying at speeds of up to 40mph, using their weight to crash through the tree canopies. But they come a cropper slamming up against 10ft-high wire deer fences, which can cause mortal injury.

Poole says that the RSPB's Abernethy National Nature Reserve is a key site for the birds, now holding eight per cent of the UK population. "We've used it for landscape-scale management trials and conservation research. Marking the fences with wooden droppers can reduce fatality by 64 per cent, though the only real solution is to remove them altogether."

Other measures have included restoration of bog woodland habitats and field-layer management by cutting or burning. Overgrazing by deer is another issue, because it not only reduces the availability of blaeberry, but also the habitats for insects, a key food source if the hen is to be able to rear the chicks successfully.

Human disturbance, caused by those curious to see these remarkable birds, is a further issue, and is the reason why a "safe" viewing site was set up at Abernethy's Loch Garten Osprey Centre. Successful measures at Abernethy that have helped the capercaillie are increasingly being deployed elsewhere in Scotland, including by private forest owners.

But the original target of the project was to have the population up to 5,000 by 2010, and this isn't going to happen, admits Poole. "Still, it shouldn't prevent us having aspirations for the future. Five thousand is a sustainable number for the species in the long term. A smaller figure would leave them more vulnerable to extinction." Capercaillies aren't out of the woods yet, but at least they are still in there fighting.